The present invention relates to shielded electric cables for the transmission of small signals through the cables and particularly an improved shielding for the cables and method of making the cables.
It is common practice to provide a shielded cable for transmitting small signals. A shielded cable usually includes a core of one or more insulated conductors enclosed within at least one conducting layer. The shielding resists signal leakage from the core and eliminates or reduces the interfering effects of extraneous electrical fields. One type of shielded electric cable commonly used consists of a center conductor having a foam dielectric extending therearound to form a core. A first shield is provided by a multiple layer tape wrapped therearound. The tape comprises an elongated ribbon of insulting material with elongated metallic strips bonded to each side to sandwich the insulating material therebetween. One commercial form of such tape comprises a layer of aluminum foil, a layer of polypropylene and another layer of aluminum foil with or without an adhesive backing. It is also common to provide a second metallic shield formed from copper or aluminum braid which is then provided with an outer cover or jacket of non-metallic material. Shielded electric cables of the foregoing type are provided with standard electric connectors having a standard diameter selected to accommodate the braided shielded cables. Braided shields because of the spaces between the wire braids have the disadvantage of providing less than 100% coverage of the core. Additionally the braided shields are difficult to cut and attach to the standard electric electrical connectors thus increasing installation time and costs.
It would be desirable to provide shielded electric cables with multiple shields and use standard connectors but eliminate the conventional braided shield.